
score=int(input('输入0-100任意数字:'))
degree='DCBAAF'                        #【90,99】区间和100都对应A
if score > 100 or score < 0 :
   print('wrong  score.must between 0 and 100.')
else:
   index = (score - 60) // 10
   if index >= 0:                      #这里对应60分以上的成绩
      print(degree[index])
    
   else:
       print(degree[-1])               #60分以下,对应F